Investigating the Longterm Biomass Yield of Miscanthus Giganteus and Switchgrass when Harvested as a Green Energy Feedstock

Recent research has indicated that the leading perennial energy grasses, Miscanthus giganteus and switchgrass (Panicum virgatum) may be utilized for non-thermal energy conversion. The feedstock requirements for these conversion technologies would allow the crops to be harvested early, prior to senescence, to exploit the greater higher biomass yields that occur during the autumn. Miscanthus grown at three locations in Europe was continually harvested early and maintained its high peak yield when compared to the conventional spring post-senescence yield. At one site, where the crop was continually harvested for 6 years, the early harvest yield began to decline after four years although this yield decline did not occur when the crop was adequately supplied with additional nitrogen. The two ecoptypes of switchgrass grown at locations in Europe, responded very differently to an early harvest. Lowland switchgrass at two locations could not maintain the high peak yield even with a moderate application of nitrogen. Upland switchgrass examined at one location did sustain high peak yields for 5 years of continuous early harvest without the need for additional nitrogen. The results of this study have indicated that a continual early harvest of both miscanthus and switchgrass is possible but replacement plant nutrients must be applied to the crop to revent or limit the extent of any yield decline.